JP2785041B2 - Fluidized bed plant - Google Patents

Description

The present invention relates to a fluidized bed plant comprising a fluidized bed reactor, a solids separator and a recirculation line for performing an exothermic reaction in a circulating fluidized bed. A pipeline for introducing oxygen-containing primary gas from the bottom of the fluidized bed reactor, at least 1 m from the bottom of the reactor
A line for introducing the oxygen-containing secondary gas above and at a height of at most 30% of the height of the reactor and between the primary gas inlet and the secondary gas inlet is open to the fluidized bed reactor. 40 to 75% of the bottom of the fluidized bed reactor is covered by at least two displacement bodies (Varangungskorper) having a fuel line with a maximum height equal to half the height of the fluidized bed reactor. To a fluidized bed plant.

[Conventional technology]

The method and apparatus of operation with a circulating fluidized bed is very advantageous, especially for burning carbonaceous materials, and for many reasons relative to the method and apparatus operated with a so-called classical or conventional fluidized bed. Are better.

In particular, a basic method for the combustion process is described in German Patent Specification No. 2539546 (corresponding US Pat. No. 4,165,717). In that method, combustion is performed in two stages, with the heat of combustion being taken away by a cooling surface located in the fluidized bed reactor and above the secondary gas inlet. A particular advantage of this method is that the combustion density can be adjusted in a technically simple manner to the required power, since the suspension density and thus the heat transfer to the cooling surface in the upper reactor space are regulated.

West German Published Specification No. 2624302 (corresponding U.S. Patent No. 4,111,1
No. 58), in the case of a combustion process using a circulating fluidized bed, part or all of the combustion heat is absorbed by a fluidized bed cooler following the fluidized bed reactor, and the cooled solids are maintained at a constant temperature. It is recycled to the fluidized bed reactor. In this case, the adaptation to the required power is effected by increasing or decreasing the solids flow which is sent to the fluidized bed reactor after passing through the fluidized bed cooler.

Although the methods outlined above have been quite satisfactory, the current trend of requiring more and more heat output to the plant units creates certain difficulties in the operation of the process. The difficulty is essentially that the greater the heat output, the larger the dimensions of the reactor, especially the cross section of the reactor, so that the fuel, etc., over the entire cross section of the fluidized bed reactor in the feed area The sufficient lateral mixing required for the reaction of the oxygen with the oxygen-containing secondary gas is no longer guaranteed. As a result, a significant portion of the reaction is transferred to the upper reaction space, and in some cases, post-combustion occurs after the solids and gas have been separated by a solids separator. The above situation appears for plants with a heat output of about 300 MW or more and a bottom of the fluidized bed reactor of about 50 cm ² or more.

According to prior proposals, the problem is that 40 to 75% of the bottom of the fluidized bed reactor is covered by one or more displacement bodies whose maximum height is equal to half the height of the fluidized bed reactor. I was trying to solve it. In this case, the geometric shape of the displacement body can be substantially arbitrary. For example, in the case of a circular cross section of the fluidized bed reactor, the displacement body can be a cylinder or a truncated cone, with the center of the lower circular surface approximately coinciding with the center of the bottom surface. If the cross section of the reactor is rectangular, the displacement body can be in the form of a dam, if necessary both ends are connected to the parallel walls of the reactor, thus dividing the lower space of the reactor into two independent rooms I do. It is also possible to provide two substantially orthogonal dams, which, when connected to the reactor wall, divide the lower space of the reactor into four independent rooms.

Obviously, in the case of a fluidized-bed plant of the structure described above, operational difficulties arise when the displacement body divides the lower space of the reactor into independent rooms. That is, the bed material is then entrained from one chamber by the primary air flow and reaches the other chamber due to the internal solids circulation that is constantly occurring in the fluidized bed reactor. It is not practical to reverse or compensate for the material flow without significant control costs. Fluidizing air is encouraged to pass through "empty" rooms, impeding passage through "filled" rooms (different hydrostatic pressures on the bottom of each room) .

[Problems to be solved by the invention]

An object of the present invention is a fluidized-bed plant comprising a fluidized-bed reactor, a solids separator, and a circulation pipe for performing an exothermic process in a circulating fluidized bed. It is to provide a fluidized bed plant which guarantees satisfactory and reliable operation without need.

[Means for solving the problem]

This problem is solved by configuring the fluidized-bed plant mentioned at the outset such that the remaining bottom surface of the fluidized-bed reactor consists of a single continuous surface.

A single continuous surface is left by configuring the displacement body such that the parts of the reactor bottom are connected to each other. For this purpose, for example, a gas-permeable bottom surface is left between the displacement body and the reactor wall surface, or when the displacement body extends from the wall surface to the wall surface, the upper part is open or has a tunnel shape. What is necessary is just to make it connect between each bottom part by at least one penetration path which can be performed. The displacement body must not be formed in such a way that independent bottom parts and thus separate flow chambers are formed. Fluidization occurs at a lower rate than the main surface of the grid on the connecting surface left by the displacement body or on the base surface created by penetration.

The geometric shape of the displacement body can be selected substantially arbitrarily. For example, if the fluidized bed reactor has a circular cross section, it may take the shape of a cylinder or a truncated cone, with the center of the lower circular surface approximately coinciding with the center of the bottom surface. If the reactor cross section is rectangular, the deformation can take the form of a dam. Two substantially orthogonal dams are also possible.

It is particularly advantageous to provide a displacement body having a square or rectangular cross section. In that case, the exact geometric shape can be deviated to some extent, for example, the corners can be rounded.

The displacement body can be made from refractory materials commonly used for furnace structures. The displacement body may also be made of membrane-like or finned walls through which the refrigerant passes, which walls are coated with a compacted material on the side facing the reactor space for protection. The displacement body is firmly connected to the reactor and forms one structural unit together with the reactor.

Since the introduction of the material capable of performing the exothermic reaction is performed from a plurality of introduction devices, the material is separately supplied to each segment formed in the lower reaction space.

According to a preferred aspect of the present invention, the displacement body has fuel introduction means. The fuel introduction means can be arranged at a plurality of heights as required. This ensures good distribution of the fuel.

According to the present invention, the fluidized bed plant has oxygen-containing secondary gas introduction means arranged at a plurality of heights, and has a plurality of secondary gas introduction inlet openings at each height. This makes it possible to supply the secondary gas to each room or room area from the inlet in the wall and inside of the fluidized bed reactor. This ensures an optimal mixing of the secondary gas.

If the secondary gas is introduced via a line in the wall of the fluidized bed reactor, the top of the displacement body should be above this line. If the secondary gas is introduced from a plurality of positions in a vertical relationship, the displacement body must extend at least above the height of the lowest introduction line.

According to another preferred embodiment of the present invention, the displacement body is configured such that its cross-sectional area decreases upward. Due to this and in combination with the embodiment just described, the flow velocity in the reactor area with the displacement body varies only within a certain range despite the introduction of secondary gas.

The principle of a circulating fluidized bed used in a fluidized bed plant is characterized by the existence of a distribution state without a clear boundary layer, in which the high-density phase is separated from the gas space above it by a clear density step. In contrast to "classic" fluidized beds. Although there is no density step between the dense phase and the overlying dust space, the solids concentration decreases from bottom to top in the reactor.

Defining operating conditions in terms of Froude number and Archimedes number gives the following ranges: And 0.01A _r 100, where It is.

In the formula, u is relative velocity (m / s) _Ar is Archimedes number _Fr is Froude number P _g is gas density (kg / cm ³ ) P _k is density of solid particles (kg / cm ³ ) d _k is spherical Particle diameter (m) V is kinematic viscosity (m ² / s) g means gravitational constant (m / s ² ).

The exothermic reaction takes place in two stages with oxygen-containing gases introduced from different heights. The advantage of this reaction is "moderate"
The overheating phenomenon is avoided, and NO _x generation is substantially suppressed. During this reaction,
The upper oxygen-containing gas introduction position should be sufficiently separated from the lower introduction position so that the oxygen content of the gas introduced at the lower position has already been consumed.

If steam is desired as the heat of the process, according to a preferred embodiment of the present invention, the average suspension density above the secondary gas inlet is adjusted by adjusting the amount of fluidizing gas and secondary gas to 15 to
At 100 kg / cm ³ , the heat of reaction is absorbed by the free space of the fluidized bed reactor above the secondary gas inlet and / or the heating surface provided on the wall of the fluidized bed reactor. Such a method of operation is described in German Patent Specification No. 2539546 and corresponding U.S. Pat.
No. 17 describes it in detail.

The gas velocity in the fluidized bed reactor above the secondary gas inlet is generally greater than 5 m / s under normal pressure and can be up to 15 m / s. The ratio between the diameter and the height of the fluidized bed reactor should be chosen such that the residence time of the gas is between 0.5 and 8.0 seconds, preferably between 1 and 4 seconds.

This method of operation has the particular advantage that the process heat gain can be varied very easily by varying the suspension density in the furnace space of the fluidized bed reactor above the secondary gas inlet.

The predetermined heat transfer is related to the operating conditions governed by a given fluidizing gas volume and secondary gas volume and the resulting predetermined average suspension density. Heat transfer to the cooling surface can be increased by increasing the suspension density by increasing the fluidizing gas amount and, if necessary, the secondary gas amount. By increasing the heat transfer,
At a substantially constant combustion temperature, it is possible to remove the amount of heat resulting from the increase in heat output from combustion. The required amount of oxygen based on the increase in combustion output is almost automatically filled by the amount of fluidizing gas used for increasing the suspension density and, if necessary, the amount of secondary gas.

Similarly, in order to adapt to low process heat requirements, the combustion power is adjusted by reducing the suspension density in the furnace space of the fluidized bed reactor above the secondary gas inlet. Reducing the suspension density also reduces heat transfer, thereby reducing the amount of heat removed from the fluidized bed reactor. Thus, the heat output from combustion is reduced essentially without a change in temperature.

According to another more universally preferred embodiment of the invention, the fluidized bed plant comprises at least one fluidized bed cooler coupled via a solids supply line and a solids recirculation line. . Above the secondary gas inlet of the fluidized bed reactor the average suspension density by adjusting properly the fluidizing gas amount and the secondary gas amount is adjusted to 10~40kg / cm ^3,
The hot solids are discharged from the circulating fluidized bed, cooled by indirect and direct heat exchange in a fluidized state, and at least a portion of the cooled solids is recycled to the circulating fluidized bed.

This embodiment is disclosed in detail in West German Offenlegungsschrift 26 24 302 and corresponding US Pat. No. 4,111,158.

In this case, to keep the temperature constant, it is only necessary to substantially eliminate the hot solids discharge and the cooled solids without substantially changing the operating conditions in the fluidized bed reactor, and in particular without changing the suspension density. Achieved by adjusting the amount of recirculation. Depending on the power output and the reaction temperature selected, the recycle rate is higher or lower. This temperature is arbitrarily adjusted from a low temperature slightly above the ignition limit to a very high temperature limited by the softening of the reaction residue. This temperature can be about 450-950 ° C.

In that case, most of the heat generated by the exothermic reaction is absorbed by the fluidized bed cooler connected to the solids side, and the heat is transferred to the cooling register existing in the fluidized bed reactor and assuming a sufficiently high suspension density. Heat transfer is not so important,
According to the method of the present invention, the suspension density in the region above the secondary gas inlet in the fluidized bed reactor can be kept low, and thus the advantage that the pressure drop over the fluidized bed is relatively small is obtained. . On the other hand, heat is absorbed by the fluidized-bed cooler under conditions where very high heat transfer, for example 300-500 Watt / m ^2, takes place.

The temperature in the fluidized bed reactor is adjusted by recirculating at least a partial stream of the cooled solids from the fluidized bed cooler. For example, the required cooled solids substream is fed directly to a fluidized bed reactor. Furthermore, the exhaust gas can also be cooled, for example by the supply of cooled solids supplied to an air conveyor or a fluidized heat exchanger, which solids are later separated from the exhaust gas and recycled to the fluidized bed cooler. You. As a result, the heat of the exhaust gas also enters the fluidized-bed cooler. It is particularly preferred to supply the cooled solids to one part stream directly and the other part stream to the fluidized bed reactor after cooling the exhaust gas.

Also in this aspect of the invention, the gas residence time and gas velocity above the secondary gas inlet at normal pressure and the supply of fluidizing gas and secondary gas are consistent with the same parameters of the previously described aspect.

Cooling of the hot solids leaving the fluidized bed reactor takes place countercurrently with the gas stream in a fluidized bed cooler having a plurality of communicating cooling chambers containing interconnected cooling registers.
This allows the combustion heat to be absorbed by a relatively small amount of coolant.

According to another aspect of the fluidized bed plant with a fluidized bed cooler, the fluidized bed cooler is structurally integrated with the fluidized bed reactor. In that case, the fluidized bed reactor and the fluidized bed cooler share a suitably cooled wall with an opening for flowing the cooled solids into the fluidized bed reactor.
In that case, as explained above, the fluidized-bed cooler can have multiple cooling chambers, but the fluidized-bed cooler can also consist of multiple units with cooling surfaces. Each unit has a common wall with the fluidized bed reactor, which has an opening for passing solids and an independent solids supply line. Such a device is disclosed in EP-A-206066.

The universal utility of an arrangement with a fluidized bed cooler is that almost any heat carrier material can be heated in the fluidized bed cooler. Generating steam in various forms and heating the heat carrier salt are of particular importance from a technical point of view.

Within the scope of the present invention, air as the oxygen-containing gas,
Oxygen-enriched air or industrial pure oxygen is used. Finally, if the reaction is carried out under pressures up to 20 bar, the power can be increased.

In the fluidized bed plant of the present invention, all self-combustible materials can be used in principle. Examples are all types of coal, especially low-grade coal, such as coal-washed garbage, sludge coal, salt-rich coal, but also lignite and oil shale. This plant can be used for roasting sulfide ore or concentrate.

The present invention will be described in detail with reference to the accompanying drawings and embodiments.

FIG. 2 schematically shows a fluidized bed reactor 1. The bottom surface is partially covered with a prism-like displacement body 7 to form a number of fluidizing grids 6. The displacement body 7 has a secondary gas opening 11 in an upper region and a fuel supply line 3 in a lower region.

FIG. 1 shows various examples of the shape of the displacement body 7 having a circular cross section or a rectangular cross section in a fluidized bed reactor.

The fluidized bed reactor 1 of FIG. 3 has a heating surface 2 shown as a membrane wall. The lower reaction chamber 8 is divided into four parts (two parts parallel to the dam and one part before and after the dam) by the dam-like displacement body 7. The grid 6 supplies the oxygen-containing fluidizing gas, the line 3 supplies the fuel, and the line 9 supplies the oxygen-containing secondary gas. Additional secondary gas is supplied from the pipe 10 and the secondary gas opening 11, and additional fuel is supplied from the pipe 3. The gas-solid suspension is discharged from line 4.

〔Example〕

 The coal was burned with air to produce saturated steam.

The fluidized bed reactor 1 of the fluidized bed plant has a bottom of 12.5m × 10.
The height was 1m and the height was 30.5m. The bottom was covered by a displacement body 7 having a 8.5 × 8.1 m bottom so that four parts with a fluidizing grid 6 were obtained. Two parts each having a width of 2 m extend parallel to the longer wall of the reactor, and two parts each having a width of 1 m are located between each end of the displacement body 7 and the reactor wall. I did it. The displacement body 7 had a prism-like shape with a height of 6.8 m.

The entire wall of the fluidized bed reactor 1 was lined with a water-cooled membrane wall. The wall of the displacement body 7 was also formed as a water-cooled membrane wall, and the side facing the reactor was protected with a refractory material.

The fluidized bed reactor 1 has a total of 110.4 t / h of coal having a calorific value H _{u of} 15.9 MJ / kg and an average particle size of 0.2 mm, and coal stone 1 having a substantially same particle size.
0.4t / h from a total of 6 pipes 3 to 100 ℃ air 11,040Nm ³ / h
Supplied by As fluidizing gas, fluidizing grid 6
From 280,000 Nm ³ / h. A total of 206,000 Nm ³ / h of 260 ° C. air was further supplied from the secondary gas lines 9 and 11. This supply is 2m above the fluidizing grid 6.
(51,500Nm ³ /h),4.6m(51,500Nm ³ / h) and 7.3m (103,
000Nm ³ / h) at three levels.

Under the selected operating conditions, the temperature in the fluidized bed reactor 1 is
850 ° C. 140 bar of saturated steam corresponding to a heat output of 102 MW was obtained on the heating surface 2 and on the membrane wall of the displacement body 7.

[Brief description of the drawings]

FIG. 1 is a plan view showing various examples of the shape of a displacement body having a circular cross section or a rectangular cross section in a fluidized bed reactor. FIG. 2 is a perspective view of a lower region of the fluidized bed reactor having a displacement body.
The figure is a longitudinal sectional view of a fluidized bed reactor. In addition, in the code | symbol used for drawing, 1 ... Fluidized bed reactor 2 ... Heating surface 3 ... Supply pipe line 6 ... Fluidization grid 7 ... Displacement body 8 ... Reaction chamber 11 ... Secondary gas An opening.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Carrell Fiddler 6350 Bad Neuheim Frankfurter Strasse 51 (56) References JP-A-61-217616 (JP, A) JP-A-61-217617 (JP) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) F23C 11/02 313 F23G 5/30 B01J 8/24

Claims (4)

(57) [Claims] 1. A fluidized-bed plant for performing an exothermic reaction in a circulating fluidized bed, comprising a fluidized-bed reactor, a solids separator and a recirculation line, wherein the upper part of the reactor is supplied to the separator. The solids separated by the separator are recirculated to the reactor via a recirculation line, and the reactor 1 is subjected to the following (a). (E) a fluidized-bed plant comprising a fluidizing grid 6 on the bottom surface of the reactor 1, through which oxygen-containing primary gas is introduced into the reactor 1;
Above the grid 6, there is a fluidized bed of granular solids, (b) the reactor 1 has an inlet above the grid 6 for introducing solids into the fluidized bed in the reactor, (c) The reactor 1 has an inlet opening for introducing an oxygen-containing secondary gas into the flow bed, the inlet openings are arranged at a plurality of heights, and a plurality of inlet openings for introducing a secondary gas are arranged at each height. The lowest height is at least 1 m above the grid 6 and the highest height is 30
% (D) at least 1% between the grid 6 and the secondary gas inlet opening.
(E) at least two displacement bodies 7 are arranged on the bottom surface of the reactor 1, the displacement bodies 7 are separated from each other, and a grid 6 is provided between the displacement bodies. And the grid 6 constitutes a single continuous surface, and 40 to 75% of the bottom surface of the reactor 1 is covered with the displacement bodies 7, and each of the displacement bodies 7
Is higher than the minimum height of the secondary gas inlet opening and does not exceed 1/2 of the height of the reactor 1 above the grid 6, and each displacement body 7 is connected to a fluidized bed in the reactor. It has an inlet opening 11 for introducing an oxygen-containing secondary gas. 2. The fluidized bed plant according to claim 1, wherein the cross section of the displacement body 7 is square or rectangular. 3. The fluidized bed plant according to claim 1, wherein the displacement body has fuel introduction means arranged at a plurality of heights as required. 4. The fluidized bed plant according to claim 1, wherein the cross-sectional area of the displacement body 7 decreases upward.